In many applications utilizing steam as a source of power or heat energy, the particular application must receive steam at an operating pressure and temperature substantially below the pressure and temperature of the steam supplied by the available steam source. The pressure or temperature, and frequently both, of the available steam supply must be reduced to the levels specified for proper or efficient operation of the particular application. Examples of processes or equipment utilizing steam at a reduced pressure and temperature relative to the typical steam supply source are drying rolls, kettles, auxiliary steam sources, and the like.
Steam valves which control the amount of steam flowing to a utilization device are well-known to those skilled in the art. Also known in the art are devices which reduce the steam temperature or superheat of flowing steam by injecting water into the steam flow, causing the superheated steam to lose heat energy by heating and vaporizing the desuperheating water. The necessary amount of desuperheating water depends not only on the required reduction in superheat of the supply steam, but also on the amount of steam. Thus, the amount of desuperheating water must be adjusted in response to changes in the volume of steam supplied, or else the desired level of desuperheating is not maintained. Where separate valving apparatus is employed to control the amount of steam applied to an application, and to dependently regulate the amount of desuperheating water supplied to that flow of steam, those skilled in the art recognize the need for correlating the flow of those two fluid variables.
Valve apparatus is known which attempts to control both the flow of steam and the flow of desuperheating water in a correlated manner. One such valve is shown in U.S. Pat. No. 2,254,472 to Dahl, which combines a steam-controlling plug valve with a separate valve for supplying quench liquid to the controlled steam flowing past the plug valve, both valves being operated by a single actuator. However, this valve apparatus is not designed to modulate the flow of "quench" or desuperheating liquid, and is unsuitable for applications requiring a selectably variable supply of steam and a functional correlation between the amount of steam passed by the valve and the amount of desuperheating water added to that steam.
Other steam valves have been proposed which condition steam by regulating both the amount of steam and the amount of desuperheating liquid, but such steam conditioning valves of the prior art generally have proved less than satisfactory in actual practice.